particle count - technique for detecting and categorizing particles in a used lube oil resulting from wear or contamination. In the test, an oil sample flows through a small orifice with a light source on one side and an optical sensor on the other. The pulse gene rated by interruption of the light source is proportional to the size of each particle. Large particles, greater than 10-15 microns, portend fatigue-related catastrophic equipment failure. See chromatography, ferrography, infrared analysis, spectrographic analysis.